This invention relates to a solvent extraction process for separating aromatic hydrocarbons from hydrocarbon mixtures which consist of aromatic hydrocarbons admixed with other hydrocarbon species such as paraffins, branched paraffins, cycloparaffins and/or olefins using ethoxylated polyol solvents having a number average molecular weight range from about 250 to about 1100.
It is known that both extraction and distillation techniques have been employed in separating particular hydrocarbon species, e.g., the aromatic hydrocarbons, from petroleum hydrocarbon mixtures having narrow boiling point ranges. For such mixtures, solvent extraction techniques have been employed. These techniques have problems, one of the more significant being the difficulty in choosing a solvent with high capacity for the aromatic hydrocarbon species to be separated as compared with those hydrocarbon species not desired. Most selective solvents particularly those which are selective for aromatic materials will also dissolve significant proportions of non-aromatic hydrocarbon species.
It is desired to treat the petroleum fractions in such a manner as to separate an aromatic rich stream from the saturated and olefinic aliphatic hydrocarbons. The aromatics have very high octane numbers and are useful for blending into motor gasoline. This is of particular value since leaded gasolines are being phased out of use. In addition, such aromatics as benzene, toluene and the zylenes are valuable feedstocks for a wide variety of used in chemical industry. The raffinates can be used as components in jet fuel or heating oils or as feed to catalytic reforming. Thus, over the years, there has been a continuing search for solvents which are selective to aromatic hydrocarbons only and have a high solvent capacity for said aromatic hydrocarbons and, at the same time, dissolve very little, if any, of the non-aromatic hydrocarbon species.
A number of selective solvents have been proposed and described for the extraction of aromatic hydrocarbons from mixtures of aromatic and non-aromatic paraffins, olefinic and naphthenic hydrocarbons. The use of alkylene oxide adducts of phenyl glycidyl ether as selective solvents is disclosed in U.S. Pat. No. 3,379,788. The use of mixed alkylene oxide adducts of ethylene or propylene glycol is disclosed in U.S. Pat. No. 2,834,820. The use of di-ethylene glycol, triethylene glycol and tetraethylene glycol is disclosed in U.S. Pat. Nos. 2,302,383; 2,711,433; 2,803,685; and 3,037,062.
The use of di, tri and tetraethylene glycols as aromatic extracts has attained widespread usage in industry. These diols had a fair balance of properties which permitted the selective extraction of aromatics and rejected the aliphatic hydrocarbons. Nevertheless these compounds did suffer from having low capacity values and so required high solvent to feed ratios. Consequently increased plant sizes and equipment were needed to handle the large volumes of solvents needed.
The solvents of this invention have a higher capacity for aromatics than the diols of the prior art. By replacing the solvents of the prior art with the solvents of this invention in existing plants and at existing flow rates, dramatically increased yields of aromatics can be obtained.
Used in a new plant, the solvents of this invention would require considerably less plant size and equipment for the same amount of solvent as below since about twice as much aromatics can be extracted.